1. Field of the Invention
The present invention relates to a new and novel method of dispersing channelized 2:1 clays (attapulgite and sepiolite) and breaking down the clay particles to form gels in fertilizer suspensions. The invention consists of using sonic energy, rather than mechanical energy such as that imparted by a pump or agitator, to create the necessary gel. As stated supra, the instant sonic gelling method is effective for use with all sepiolite or attapulgite containing fertilizer suspensions, including systems containing ionic, and/or anionic materials, having solids as well as no solids, and having dry or predispersed fluid-clay materials used in their manufacture. The present invention is particularly effective and applicable for use with systems where dry clay is added to ionic solutions without undissolved solids present, i.e., systems otherwise of a type in which mechanical shear requirements are prohibitive in terms of energy and retention time.
2. Description of the Prior Art
Some investigators have discovered used of sonic agitation which result in reduction of particle size of solids contained in fluid media. Thus, in his U.S. Pat. No. 4,412,842, Klayer, Nov. 1, 1983, obtained size reduction of coal slurred in water. Treatment of clay suspensions with ultrasonic energy has been studied in drilling mud applications. Kruglitskii et al, in Ukr. Khim. Zh. (Russ. Ed.), 40 (2), 141-145, 1974 stabilized montmorillonite suspensions with ultrasound and a water-soluble acrylic polymer. In studies of the present invention, we found that the sodium bentonite form of montmorillonite did not respond to ultrasound by forming a gel and was thus unsuitable for the method of the present invention. This result was expected because sodium bentonite swells when mixed with water rather than gelling by breaking apart of the clay particles as do, for example, attagpulgite and sepiolite.
Also, Kruglitskii et al (Tr. Ukr. Nauch.-Tekh. Konf. Termo-Soleustoichivym Promyvochnym Zhidtk Tamponazhnym Rastvoram, 1st, Meeting Date 1968, Volume 1, 185-92. Edited by: Kruglitskii, N. N. "Naukova Dumka": Kiev, Ukr. SSR.), treated palygorskite as well as montmorillonite with ultrasound to improve the physical-mechanical properties of drilling fluids. Kruglitskii stabilized a 10 percent (by weight) palygorskite suspension in water with the addition of up to 0.1 percent (by weight) NaOH and the use of ultrasound. Kruglitskii does not described the methods or type of ultrasonic equipment used, nor is the palygorskite further identified as to source. A sonification time of 8 minutes, however, was required to achieve maximum stabilization, and furthermore no improvement, in fact, even a slight decrease in stability, was obtained during the first 4 minutes as indicated by the curve in Kurglitskii's first graph. Whether this long retention time and lack of result during its first half was due to the relatively high clay concentration (the experimental drilling fluids were intended for use in deep and super-deep oil and gas wells) is unknown. Based on results of tests made in developing the present invention and described below, however, it is possible that Kruglitskii's procedure employed an insufficient power density (watts per milliliter of clay-water mixture) because the method, clay, and power density levels of the present invention result in an increasing clay gelling action beginning practically instantly after starting sonification. This rapid response is illustrated in FIG. 1 infra, showing the increase in viscosity due to sonic irradiation of a mixture containing 3 percent attapulgite clay in 10-34-0 grade ammonium polyphosphate solution fertilizer. (The procedure used in obtaining the data for this graph is described more fully in Example I, infra.) FIG. 1 is also introduced and discussed more fully infra. Thus, it is shown that the sonic treatment immediately began gelling the clay and increased the viscosity from about 50 (54) centipoises to about 80 centipoises in only 5 seconds and further to about 250 (244) centipoises in only 20 seconds. The usefulness of this rapid response, which is obtained following the teaching of the instant invention and which results in shorter retention times which, in turn, means that smaller vessels can be used, can be easily appreciated by all those skilled in this art. Obviously, similar teachings were not indicated in the results of Kruglitskii.
Agabal'yants, in Kim Teknol. (Kiev), (1), 13-15, 1975 used sonification as an alternative to chemical treatment to stabilize palygorskite drilling mud. He indicated that he obtained dispersion of the clay and increased viscosity after a period of 6 minutes retention time and at a concentration of 10 percent clay with the further proviso that no dissolved salts were present in the mud. The principal purpose and objective of his experiment was to avoid the use of expensive chemical treatment for stabilization. Thus the results of Agabal'yants do not infer or indicate that sonification would be useful for the preparation of fertilizer suspensions, which always contain high levels, usually saturation levels, of highly soluble ionic fertilizer salts (dissolved). As indicated supra, attapulgite clay strongly resists gelling in the presence of ionic solutes.